Minimally invasive surgical procedures, such as percutaneous transluminal coronary angioplasty (PTCA), have become increasingly common. A PTCA procedure involves the insertion of a catheter into a coronary artery to position an angioplasty balloon at the site of a stenotic lesion that is at least partially blocking the coronary artery. The balloon is then inflated to compress the stenosis and to widen the lumen in order to allow an efficient flow of blood through the coronary artery.
Following PTCA and other stenotic treatment procedures, a significant number of patients experience restenosis or other vascular blockage problems. These problems are prone to arise at the site of the former stenosis.
In order to help avoid restenosis and other similar problems, a stent may be implanted into the vessel at the site of the former stenosis with a stent delivery catheter. A stent is a tubular structure which is delivered to the site of the former stenosis or lesion and compressed against vessel walls thereat, again with a balloon. The structure of the stent promotes maintenance of an open vessel lumen. The stent can be implanted in conjunction with the angioplasty.
Stents can also be used to provide for local delivery of agents. For example, radiotherapy and drug delivery treatments applied to the site of the former stenosis following angioplasty have been found to aid in the healing process and to reduce significantly the risk of restenosis and other similar problems. Local delivery of agents is often preferred over systemic delivery of agents, particularly where high systemic doses are necessary to achieve an effect at a particular site. High systemic doses of agents can often create adverse effects. One proposed method of local delivery is to coat the surface of a stent with an agent.
A stent is typically coated with a primer layer and an agent layer. The primer layer is applied between the stent and the agent layer to improve adhesion of the agent layer to the stent. In some cases, the agent layer may be applied directly to the stent.
Spray coating is commonly used to apply a layer of coating to a stent. A spray coating apparatus typically includes a spray nozzle and a pump that supplies a coating substance from a reservoir to the spray nozzle. The coating substance is ejected through the nozzle to create a plume of coating substance.
During coating operation the stent is supported by a stent support, and the stent support and stent rotate about the axis of the stent support. The stent support is also configured to axially or linearly translate the stent through the plume of coating substance. Alternatively, the nozzle can be translated along the axis of the stent as an alternative to or in addition to axially translating the stent. The coating substance is deposited on the stent as the stent is translated through the plume of the spray nozzle from one end to the other end of the stent. After the spraying operation is stopped, the amount of coating substance on the stent is measured to determine whether it is within a required range. If the amount of stent coating is outside of the range, the stent is considered defective and may be discarded.
The amount of stent coating is typically determined by comparing the weight of an uncoated and coated stent. Currently, the weighing of a stent requires manual manipulation of the stent and stent support. The operator must remove the stent from the stent support and place the stent on a scale to measure stent weight. The operator may need to put the stent support aside if she must manually operate the scale. After a successful measurement of stent weight, the operator picks up the stent support and mounts the stent on the stent support.
This manual procedure has several drawbacks. For example, manual manipulation of the stent may damage the stent or stent coating. For another example, contamination of the stent may result from contact with operator gloves or areas of the weighing station that are not cleaned regularly. Manual loading/unloading of the stent from the delicate scale may damage the scale by overloading or bending the scale post. The damage may cause catastrophic failure of the scale or inaccurate readings. Additionally, the manual procedure is time-consuming. The dismounting of a stent from a stent support and the mounting of a stent on a stent support are delicate tasks, and the operator must be careful to avoid damaging the stent or stent coating. Furthermore, if the operator needs to put the stent support aside to manually operate the scale, she may pick up a wrong stent support and mount the stent thereon. This may have grave consequences because the stent support usually has information identifying the type of stent mounted thereon and the drugs coated on the stent.
Therefore, there is a need for a method and apparatus for efficiently and automatically weighing a stent with minimum risk of damaging the stent or stent coating or mounting the stent on a wrong stent support.